Novel amorphous guanidine silicates,and compositions thereof with synthetic resins



United States U.S. Cl. 260-59 5 Claims ABSTRACT OF THE DISCLOSURE Thepresent invention relates to compositions of matter containing as anessential ingredient, stable, non-crystalline guanidine silicates havinga molar ratio of guanidium ions to silicate ions of from 1.5 to 0.65.These compositions are characterized by the fact that they are amorphousand soluble in water, giving aqueous solutions which may be highlyconcentrated. The dried or dissolved materials are used as adhesives,binders, and film-forming agents. These guanidine silicates are preparedby bringing together a source of guanidinium ions and colloidal silicaunder closely controlled reaction conditions. Close process control isnecessary to produce the novel amorplrous compounds of this invention.

BACKGROUND OF THE INVENTION This application is a continuation-in-partof copending application Ser. No. 648,216, filed June 23, 1967, and nowabandoned.

The present invention relates to guanidine silicates. The novelcompounds of this invention are characterized in that they are amorphousand highly water soluble. Alkali silicates either alone or incombination with other materials have been used for some time as bindersfor sand and other refractory materials in casting processes, asadhesives, as film-forming agents and in coatings. In the past, alkalimetal silicates have been used for most of the above applications wheresoluble, basic silicate was required, however, difficulties associatedwith the removal of the alkali metal component have prevented their widespread acceptance. A basic silicate combining the desired properties ofwater solubility and easy removal of the cation component has beensought for many applications.

It has now been discovered that silicates of the organic base guanidinecan be prepared in an amorphous, highly soluble form. Guanidinesilicates are known to the art. However, the only known guanidinesilicates are crystalline materials having very limited watersolubility. Such crystalline guanidine silicates and processes for theirpreparation are disclosed in U.S. Patent 2,689,245 to Reynold C.Merrill.

SUMMARY OF THE INVENTION According to this invention, amorphousguanidine silicates having exceptionally high Water solubility well inexcess of 15% by weight of silica in the solution have been discoveredalong with processes for their preparation. The guanidine silicates ofthe invention have a molar ratio of guanidinium ions to silicate ions offrom 1.5 to 0.65. These compositions are completely amorhpous, failingto reveal any crystalline structure even on microscopic or X-rayexamination.

The compositions of this invention differ from those of the prior art inthat they are of the order of a thousand times more soluble in waterthan the crystalline guanidine silicates of similar mole ratiopreviously described, and

may be prepared in highly concentrated solutions. The previously knowncrystalline compounds resist all attempts at concentration. Theyrecrystallize out making it impossible to maintain solutions at ambienttemperature having other than low silica concentrations.

The novel guanidine silicates of this invention may be prepared byprocesses which in general comprise contacting 'a source of guanidiniumions with colloidal silica at a high pH, a low temperature, and in thepresence of closely controlled relative amounts of guanidine and silica.The reaction must be closely controlled and variables such as theconcentration of reactants, time, temperature and pH are critical andmust be carefully maintained as will be described more fully hereinafterin order to achieve the preparation of these amorphous, solublecompounds.

THE GUANIDINE CATION The usual source of the guanidine cation isguanidine hydroxide.

Guanidine hydroxide may be prepared by techniques known to the art or bythe adaptation of techniques which have been employed to prepare freehydroxides of other strong organic bases. For example, guanidinehydroxide can be prepared by the precipitation of calcium carbonate fromsolutions of guanidine carbonate by the addition of lime, byprecipitation of barium sulfate from solutions of guanidine sulfate bythe addition of barium hydroxide, the precipitation of silver chloridefrom guanidine chloride by the addition of freshly precipitated silveroxde or ammoniacal silver hydroxide, as well as precipitations employingthe iodide or bromide of guanidine. Solutions of guanidine hydroxide mayalso be prepared by deionization of a soluble guanidine salt employingthe hydroxyl form of a strong basic ion-exchange resin.

SILICA SOURCES A variety of sources of silica may be employed in theprocesses of the invention. These include precipitated gels and powdersof colloidal amorphous silica having surface areas in excess of 20 mF/g.and preferably in excess of m. g. They also include colloidal sols ofamorphous silica having the same surface areas. Such sols, powders, gelsand precipitates can be prepared 1n a variety of ways well known to theart. These include precipitation of solutions of alkali metal silicateswith acids; followed by washing to obtain a high surface area silicagel; oxidation or hydrolysis of silicon tetrachloride; and thecontrolled polymerization and growth of colloidal amorphous silicaparticles from solutions of silicic acid or higher surface area silicasols. High surface area amorphous silica residues may also be preparedby acid leaching clay minerals, such as magnesium or aluminosilicateminerals, as well as by a variety of other techniques which are knownand practiced in the art.

Alternatively, solutions of silicic or polysilicic acids may be employedas the siliceous raw materials. These include, for example, solutionsprepared by the neutralization of dilute solutions of alkali metalsilicates with acids, followed by purification to eliminate the metalsalts produced by the neutralization. Solutions of silicic acid preparedby the deionization of alkali metal silicates with cation exchangeresins in the hydrogen form, and solutions prepared by the hydrolysis ofsilicate esters such as ethyl orthosilicate can also be used. It is onlynecessary that such silicic acid solutions have a very limitedstability, since their rate of reaction with guanidine hydroxide to formguanidine silicates is quite rapid.

Silica sols suitable as reactants may also be prepared from siliconmetal. For example metallic silicon may be reacted with concentratedaqueous ammonia solutions or aqueous solutions of amines. In addition,metallic silicon and certain silicon metal alloys are also usefuldirectly, as sources of silica, in which instance the reaction to formthe active form of silica and the reaction to form the guanidinesilicate compositions of this invention from such raw materials occuralmost simultaneously. For example, solutions of guanidine hydroxid maybe reacted with finely divided silicon metal.

Alternatively, guanidine cations can be formed in situ and reacted withsilicate anions at the moment of their generation to form thecompositions of this invention in a single step. The guanidine form of acation exchange resin can be prepared by contacting the hydrogen form ofthe resin with guanidine hydroxide or guanidine carbonate.

Thus, a guanidine cation exchange resin can be reacted with an alkalimetal silicate solution having mole ratios of metal cation to silicabetween 1.5 and 0.65 directly to generate the compositions of theinvention in a single rapid operation.

Also, solutions of guanidine carbonate could be reacted with asuspention of a calcium silicon alloy, again observing the relativeproportions of the guanidine carbonate and calcium silicon alloy toobtain a guanidine silicate and calcium carbonate as products. After thereaction, the product would be separated from the insoluble calciumcarbonate by filtration.

THE REACTION A most critical aspect of the process required to obtainthe products of the invention is close control of the relativeproportions of the reactants. Close control must also be exercised overreaction conditions. It is critical for the successful operation of theprocesses of this invention, and to obtain the products thereof, thatthe mole ratios of guanidine hydroxide to silica in the reactingsolution fall within the limits of from 1.5 to 0.65. When mole ratios ofguanidine to silica higher than 1.5 are employed, water-insolublecrystalline guanidine silicate precipitates are formed at relatively lowconcentrations of silica. It seems possible that such silicates maycontain direct silicon to nitrogen bonds, or perhaps a multiplicity ofsuch bonds. In any event, these crystalline, water-insoluble silicatesare always obtained at low silica concentrations when mole ratios ofguanidine to reactive silica higher than about 1.5 to 1 are used.

When mole ratios of guanidine to silica less than 0.65 are used,undesirably rapid increases in the viscosity of the resulting solutionsoccur.

When the mole ratio of guanidine to silica is below 0.65, and especiallyif highly reactive sources of silica such as silicic acid or polysilicicacid are used, it is possible to obtain relatively concentrated,although highly viscous, metastable solutions as a result of the initialinteraction between the guanidine hydroxide and reactive silica. Whenless reactive forms of silica such as colloidal silica sol particles orsilica gel particles are used at these mole ratios, the excess silicainitially fails to react. When it finaly does react, gels and solutionsof excessively high viscosity are obtained.

Solutions having below 0.65 mole of guanidine per mole of silica are notindefinitely stable, and the stability upon storage is a function ofboth the mole ratio and the solids concentration. In some circumstances,it is useful to have a material which has a lower mole ratio than 0.65and these may be prepared but they have only a limited stability of froma few hours to about a week. In such circumstances, it is possible toprepare materials having ratios lower than the recommended lower limit,and these may be employed so long as stability is not a critical factor.However, below 0.5 mole of guanidine per mole of silica, it is notpossible to prepare even temporarily, a clear ionic solution ofguanidine silicate.

A second critical factor in the operation of the processes of thisinvention, and for obtaining the novel products thereof, is a closecontrol over the time and temperature conditions for conducting thereaction between the source of guanidine hydroxide and the source ofactive silica. The time required depends both on the temperature and onthe relative reactivity of the source of silica employed. For example,if silicic acid or very low polymers of silicic acid are used as thereactive silica source, extremely short reaction times at roomtemperature are sufiicient to prepare the guanidine silicatecompositions of the invention. With less reactive silica sources, suchas silica sols and silica gels and powders, reaction times are longerand become undesirably long at room temperature for the lower surfacearea sources. Thus, reaction times as long as from 6 to 24 hours or evenlonger may be required at room temperature and below when using the lessreactive forms of silica.

These times may be shortened by rasing the temperature of the reaction,but caution must be employed that it is not too high and especially thatthe reaction mass does not remain at high temperatures over extendedperiods of time. This is because the guanidine cation itself is subjectto a hydrolysis reaction at elevated temperatures, wherein it is firsthydrolyzed to urea and ammonia, and is ultimately hydrolyzed to ammoniumcarbonate. For this reason, it is undersirable to employ reactiontemperatures above 100 C. The preferred range is 25 to C. It is alsoundesirable to run the reaction temperatures below 25 C. because of thepossibility of forming crystalline guanidine silicates which willprecipitate as highly water insoluble compounds.

Even with the least reactive of the silica raw materials, reaction timesat this temperature are seldom in excess of a few minutes.

The time of reaction follows an inverse relationship to the temperature,and is also directly related to the reactivity of the silica rawmaterial employed. As previously noted, monomeric silicic acid and lowpolymers of silicic acid react very rapidly even at room temperatures,wheras reaction times of the order of an hour are required with the lessreactive silica sources at temperatures in the neighborhood of 75 C.

The proper pH for formation of the soluble guanidine silicates of thisinvention is in excess of 10.5, and preferably in excess of 11.Guanidine hydroxide solutions which are sufficiently dilute to give pHvalues lower than this do not give satisfactory products. Below pH 11,rates of reaction are considerably slower than are desired, particularlywhen employing amorphous silica sols or powders as raw materials.

Solutions of guanidine hydroxide have only a limited stability. Thisstability is determined both by the temperature and by the concentration.of guanidine hydroxide. If highly reactive solutions of silica are usedsuch'that temperatures of the reaction are low and reaction times areshort, it is possible to use solutions of guanidine hydroxide containingup to 60% by weight. It is desriable to store very concentratedsolutions of guanidine hydroxide at a temperature near 0 C. to minimizedecomposition of guanidine. When less reactive sources of silica areused which require higher reaction temperatures, it is desirable to useless concentrated solutions of guanidine hydroxide as a reactant.Solutions containing about 30% by weight of guanidine hydroxide arerelatively stable for periods of time of a few hours and those of 10% orless for 24 hours or more. Solutions of about 10 to 40% concentrationare preferred, and these hydrolyze only to a negligible degree withinthe required reaction time of even the least reactive of the silicasources to be employed as raw materials.

THE PRODUCTS The products of the above-described reaction arenoncrystalline (amorphous) guanidine silicates. They can be prepared atconcentrations in excess of 15% by weight of silica in solution, andthese solutions are generally quite stable for indefinite periods ofstorage. Solutions which are more dilute in silica than this are stablefor reasonable periods of time, but if the silica content is in theneighborhood of only 5 to 6% by weight, there is a tendency over aperiod of time to precipitate water-insoluble crystalline guanidinesilicates from such compositions. This may be due to the formation ofpolymeric species of silicic acid and guanidine, but in any event, itcan be avoided by concentrating to silica concentrations in excess of15% by weight of the total solution with concentrations in excess of 20%being preferred. Maximum stability occurs at mole ratios above about0.83 with mole ratios of 1 to 1 being preferred.

Concentration is accomplished in a variety of ways known to the art forconcentrating stable ionic salt solutions; for example, by reverseosmosis, by evaporation, by vacuum evaporation, by ion exclusion, and byother techniques normally employed for such purposes. It is critical,however, that the temperature not exceed 75 C. for any prolonged periodof time while such concentration is being performed. More satisfactoryresults are obtained when the temperature does not exceed 50 C. The mostpreferred technique is that of vacuum evaporation at temperatures below50 C.

Due to the exceptional water-solubility of these noncrystallineguanidine silicates, there appears to be almost no practical upper limitto the concentration of solutions which may be prepared from them. If,for example, a reasonably fluid material such as a 60% solidscomposition containing about 30% silica and having a 1 to 1 mole ratioof guanidine to silica is concentrated further by vacuum evaporationbelow 50 C., the viscosity increases in a regular fashion to form firsta viscous syrup, then a syrup of heavier consistency which can be spuninto fibers, and finally without any precipitation or clearcuttransition, the compositions are converted to a glassy, water-clear,solid film. These compositions can be redis solved in water instantly,to reconstitute the solutions of the invention. Solutions of theseamorphous guanidine silicates can be evaporated to dryness to yieldoptically clear, glassy films. No crystallinity is discrenible in thefilms either on examination with a microscope or by X- ray techniques.

As it will be more fully described hereinafter, one of the aspects ofthis invention lies in the combination of guanidine silicate in stablemixtures with alkali metal slicates such as sodium silicate, potassiumsilicate, and lithium silicate. These compositions can be formed simplyby mixing the solutions of the two silicates. They can be dried to formhard, clear, adhesive films which can be heated to a sufficienttemperature to induce the decomposition of the guanidine ion and achievevery useful results. If this heating is done rapidly, the viscous,impervious silicate mass will spontaneously foam to give inorganicfoamed structures which are useful as insulation. This foaming propertyis very useful when such mixtures are employed as binders in fireretardant intumescent paints. Alternatively, if the heating is donesufficiently slowly and decomposition products of the guanidine cationescape from the film by diffusional processes without formingmacroscopic bubbles of gas, it is possible to convert such films intodense, water-insoluble masses which have considerably higher silica toalkali metal cation ratios than the alkali metal silicates themselves.Such films and adhesive compositions are much more water resistant thanthe corresponding unmodified films containing the alkali metal silicatesalone, and also have considerably higher melting points and softeningpoints than do the alkali metal silicates. For this reason, they formmuch more satisfactory high temperature bonding agents and superiorcements, film-forming agents and binders than do the alkali metalsilicates in various types of applications where water-resistance orthermal resistance are important use characteristics. This includes suchuses as refractory binders for magnesium oxide, amorphous silica, clayminerals, alumina, and the like,

uses as binders for zinc-rich paints, uses as adhesives for boxboardapplications, and uses as binders and adhesives for roofing granules.

There are no critical compositional limits on the mixtures of guanidinesilicate and alkali metal silicates. The proportions will depend on theproperties desired in the mixture which will depend on the application.As a practical matter, 5-95 mole percent of alkali metal silicate in amixture will be preferred for most applications. Further compositions ofthis invention are mixtures of guanidine silicate in various proportionswith dispersions of colloidal amorphous silica. While such mixtures arenot indefinitely stable, they represent highly useful aspects of thecompositions of this invention, and they are sufficiently stable to giveworking lives of from a few minutes to several days depending on therelative proportions of the ingredients and other factors, which will bediscussed below.

The prior art is familiar with a wide variety of colloidal amorphoussilica dispersions in water. Such dipersions generally range inconcentration from approximately 5% SiO to 70 or SiO and in particlesize from a diameter of about 1 millimicron to a diameter of about 500millimicrons. These dispersions can be prepared by a variety oftechniques, including the oxidation of silicon tetrachloride withgaseous oxygen, followed by suspending such particles in water. Stablecolloidal dispersions of amorphous silica may also be prepared by thecontrolled polymerization and growth in aqueous solution to givespherical, dense amorphous silica particle dispersions having particlesizes ranging throughout the limits discussed above. Similar sols may beprepared by the reaction of very finely divided silicon metal withammonia or amines, as well as by the deionization of alkali metalsilicates to give reactive silicic acid which can then be nucleated andpolymerized to give dispersions of a variety of sizes. Particles of thetype discussed here may also be prepared by vaporizing and condensingsilica in an arc or by the hydrolysis of silicon tetrachloride in thevapor phase, as well as by the decomposition of clay minerals, such asby acid leaching of a mineral silicate. Such colloidal amorphous silicasols may consist of discrete spherical particles, or may, particularlyif formed from the clay minerals, have a variety of shapes which aredetermined by the nature of the mineral employed and the conditions ofdecomposition of it. Such particles may exist either as discrete unitsor as aggregates. Dispersions of colloidal silica are normally preparedand stabilized in aqueous solution by the addition of a sufiicientamount of alkaline material to maintain the pH of the dispersion withinthe range of 9 to 10.

There are two interesting variants in the' type of compositions whichcan be prepared by mixing colloidal amorphous silica dispersions withthe guanidine silicate compositions of this invention. If a colloidalamorphous silica dispersion is mixed directly into the guanidinesilicate compositions of this invention, it will first be noted that thesolutions appear to be completely compatible and remain clear, exceptfor the slight turbidity associated with the amorphous silicaconstituent. As more of the amorphous silica is introduced, a highlythixotropic solution results, and if still larger quantities ofamorphous silica are introduced, the composition forms a rigid gel.These highly thixotropic mixtures are quite useful as binders fordipping and coating compositions, since relatively thick sections can beapplied by spraying, dipping or painting on vertical surfaces and willremain on such surfaces indefinitely without running off. By reversingthe order of mixing, it is found that initially, again, a considerablequantity of concentrated guanidine silicate can be introduced intoconcentrated colloidal amorphous silica dispersions until a third of thetotal silica concentration in such a mixture is composed of silicateanions from the guanidine silicate. At this point, a very viscous andthixotropic mixture starts to form, as when the order of addition isreversed.

It is possible, however, to prepare fluid, relatively clear compositionshaving a ratio of silica from guanidine silicate and silica from acolloidal silica sol within the range where thixotropic mixtures or gelsare normally firmed. This can be done by adding an amount of a strongbase (which can be an alkali metal hydroxide or guanidine hydroxide)just sufficient to provide approximately one alkali metal or guanidinecation for each surface silanol group on the colloidal amorphous silicaparticles. The number of such groups can be determined by a measurementor an estimation of the particle size along with the concentration ofthe amorphous silica. Alternatively, it can be determined by ameasurement of the surface area of the particles, such as by nitrogenadsorption.

Thus, if relatively fluid, reasonably stable mixtures are desiredthroughout the whole range of combined proportions, this may be done byadding an amount of alkali as indicated above to the colloidal amorphoussilica dispersion, and then adding this dispersion to the concentratedguanidine silicate. Such compositions are exceptional binders. They alsoform strong and hard films and adhesives, and have a variety of specificuses which will be discussed in greater detail subsequently.

The proportions of quanidine silicate to colloidal amorphous silica inthese mixtures is not critical, but suitable proportions will be readilydeterminable by one skilled in the art based on the properties desired.The preferred range would be a mixture containing from 5-995 percent byweight of colloidal silica particles based on the total solids present.Even very small quantities of guanidine silicate can, however, bringabout extensive changes in the properties, behavior, and usefulness ofamorphous silica dispersions. For example, even a few one hundredths ofone percent of guanidine silicate can greatly accelerate the rate of gelformation of amorphous silica dispersions when these are neutralizedwith acids. The strength and pore size distributions, as well as theuniformity of such gels, are also greatly different from those obtainedin the absence of guanidine silicate. Such compositions are particularlyuseful as refractory binders for molds for casting molten metals, forbricks to be used in steel furnaces, and as high temperature catalystbinders. The complete absence of metal cations leads to exceptionalrefractory properties in such uses.

Still another useful and novel aspect of the compositions of thisinvention is mixtures of guanidine silicate with formaldehyde orwater-soluble organic molecules having a multiplicity of functionalgroups which are capable of reacting with the guanidine cation of thecompositions of the invention by condensation or addition reactions toform polymeric materials. structurally, such polyfunctional organiccompounds may be represented by the generic formula R (C) R where R andR are selected from the group consisting of carboxyl, hydroxy, amino,aldehyde, ketone of the formula ll -O-R3 where R is methyl or ethyl andterminal carbon-carbon double bonds, where n is two or greater, with theproviso that when one R is a double bond the other R is nitrile or oneof said other mentioned substituents. Thus, one of the series of novelcompositions of this invention is a mixture of amorphous guanidinesilicate with from 5 to 95 mole percent of a polyfunctional solubleorganic compound such as is described herein.

Structurally, the guanidine cations of the invention are diamides andare capable of undergoing all of the polymerization and additionreactions characteristic of thi type of functional group. They may, forexample, react with dibasic acids or with their amides, with theelimination of water or of ammonia to form polyamides, or with dibasicacid esters with the elimination of volatile alcohols to formpolyamides. The amide hydrogens on guanidine are also sufficientlyreactive to add rapidly across activated carbon-carbon double bonds andto aldehydes and ketones. For example, formaldehyde add to guanidine toform mono-, di-, and trimethylol derivatives which are analogous to themono-, di-, and trimethylol ureas, and which, upon heating will undergoadditional polymerization and condensation reactions to formthree-dimensional guanidine-formaldehyde resins which are quite similarto ureaformaldehyde resins.

Guanidine reacts by addition polymerization with activated carbon-carbondouble bonds in compounds such as acrylonitrile, acrylic and methacrylicacid and the corresponding esters and amides of these. Upon heating inaqueous solution, the nitrile group, or amide or ester groups arehydrolyzed and converted into an acid, which then can be polymerizedthrough the condensation of water to give a polyamide polymer. Similarcondensation reactions can occur between the silanol groups of thesilicic acid anions and the amide groups of guanidine, as well asbetween silanol groups on adjacent silicic acid anions. Suchcondensation and crosslinking reactions may also occur between silanolgroups and hydroxyl, amido, or ester groups which are attached to thepolyfunctional organic compounds. Through the simultaneous condensationpolymerization of guanidine with such reactive organic compounds, ofguanidine with the silanol groups on the silicic acid anions, andbetween the silanol groups of the silicic acid anions and the reactivefunctional organic compounds, complex three-dimensional polymers havinga range of properties may be prepared. Such compositions are usuallywater-insoluble and the addition of these polyfunctional organiccompounds therefore comprises one way of achieving water-insoluble filmsor bonded structures starting with guanidine silicate.

The most preferred polyfunctional reactive compounds are those whichhave an appreciable water-solubility and which can be prepared ashomogeneous solutions when mixed with the guanidine silicatecompositions of the in vention. Compounds such as acrylonitrile,polyacrylamide, maleic acid, and trimethylolurea, all of which possessrelatively high water-solubility, are some of the preferred organiccompounds for preparing this aspect of the compositions of theinvention. Ternary mixtures of guanidine silicate with colloidalamorphous silica and reactive polyfunctional organc compounds are alsopreferred compositions of this invention.

The compositions of this invention are useful in a wide variety ofapplications'such as binding agents, film-forming agents, and adhesives.In many applications they perform in a unique way not common to anyknown binder composition of the prior art.

A specific example is the use of concentrated guanidine silicatecompositions or mixtures thereof with reactive polyfunctional organicmolecules as binders for sand cores which are employed to create shapedcavities in castings prepared from molten metals. The most widely usedpolyfunctional organic binders currently available for this purpose areorganic resins, such as phenolformaldehyde resins, furfural resins,furfural-phosphoric acid resins, and furfural-urea formaldehyde resins.The amount of resin used is about 20 to percent by weight base-d on theweight of the total binder solids.

Such organic resins alone form well-bonded sand cores, and areparticularly desirable because the bond is completely decomposed by thehigh temperatures prevailing in the casting operation shortly after themetal casting has solidified. It is thus possible to easily remove theloose sand from which the fugitive binder has escaped when the castingoperation has been completed.

Unfortunately, however, these resinous compositions require relativelyelevated temperatures to develop satis factory bonding strength. Thisnecessitates the use of expensive metal patterns and complex hot coreboxes to prepare the resin-bonded sand cores. A further disadvantage isthat during the process of heating the core to cure the resin bond,undesirable dimensional changes arise as a result of the differingcoefficients of thermal expansion between the resin, the sand, and thepatterns.

A different class of core bonding agents which avoid .some of theproblems associated with resin bonded cores are the alkali metalsilicates. For example, if sand is moistened with concentrated sodiumsilicate solutions, and packed into the desired shape, it can then beset rapidly at room temperature by exposure of the moistened sand bodyto gaseous carbon dioxide. In this way, inexpense patterns of wood,rubber or plastic may be employed instead of the more expensive metalpatterns required for resin bonded cores, and simple wooden boxes may besubstituted for the expensive and complex hot core boxes. Dimensionalchanges are virtually eliminated since the curing of the compositionoccurs at the same temperature as that prevailing during the assemblingof the core. In spite of its advantages, however, sodium silicate bondedcores have been employed only to a minor degree by the casting industrybecause of several serious defects. The most serious of these is thatsodium silicate cores do not disintegrate upon exposure to highertemperatures and consequently the cores are exceedingly difiicult toremove from the cavity in the casting. A further problem is that suchcores remain quite strong and rigid at high temperatures where themetals are relatively weak. Thus, as the temperature drops, and as themetal contracts and shrinks due to its high coefiicient of thermalexpansion, the metal often tears or cracks when thin sections of themetal are located in areas where the contraction of the metal isconstrained by the core configuration. This is not a serious problemwith resin bonded cores, since after the binder has decomposed thecontracting motion of the metal can be accommodated by deformation ofthe core. In sodium silicate cores, however, the core does not deformand the metal often tears.

Guanidine silicate may be used in a fashion substantially identical tothat described above for sodium silicate. A striking property exhibitedby the compositions of this invention is that concentrated guanidinesilicates set rapidly at room temperature upon exposure to CO in afashion exactly analogous to that of sodium silicate. However, as aresult of the complete decomposition of the guanidine cation when thebonded core is exposed to the high temperatures prevailing in thecasting operation, guanidine silicate bonded cores decompose to give afreeflowing sand exactly analogous to organic resin-bonded cores. Thus,guanidine silicate seems to simultaneously exhibit the bestcharacteristics, and to avoid the worst problems, associated withprevious core binding materials known to the art. Similar behavior isalso exhibited by the guanidine silicate-reactive polyfunctional organiccompound compositions of the invention, and, in certain instances, thesemay even be superior to guanidine silicate alone in this application,since the polymers so formed decompose more slowly and at highertemperatures than does the guanidine cation itself. This is sometimesdesirable when it is required that the bond in the core disappear at aslower rate or be maintained at a higher temperature than is obtainablewith pure guanidine silicate.

Another unique application of the compositions of this invention is inthe spinning of ceramic fibers. The prior art has long soughtsatisfactory processes for preparing refractory ceramic fibers such asamorphous fused silica fibers, fibers of zircon, aluminosilicate fibers,and others. The difficulties associated with preparing such fibers canbe illustrated by the procedures which the prior art has employed toprepare relatively pure amorphous silica fibers. Because of its veryhigh melting point, in excess of l-600 C. and the very high viscosity offused silica glass, it is exceedingly expensive and very difficult tospin such fibers from a melt. In one procedure, fibers of boric oxideand silica which have lower melting points and lower viscosities havebeen spun from melts, and the boric oxide then leached out by prolongedtreatment with aqueous acidic solutions. The multiplicity of fine porescreated by the loss of the boric oxide constituent are then partiallyclosed by heating and annealing treatments. Other approaches in the arthave been to spin fibers from aqueous alkali metal silicate solutionsand leach out the alkali metal oxides with acid. All such processes havebeen expensive because of the long times required to leach out theundesirable constituents such as boric oxide or alkali metal cations.

The concentrated guanidine silicate compositions of this invention,along with concentrated mixtures of these with colloidal amorphoussilica dispersions, are viscous and thixotropic, and behave excellentlyin spinning operations. Individual fibers can be drawn from a viscoussolution by usual spinning techniques. Such fibers, once spun, have theunique advantage over prior art techniques of making fibers in that theycan be converted into pure amorphous silica glasses, simply by heating.At temperatures in the neighborhood of 300 C. and higher the guanidinecation thermally decomposes, the gases are liberated, and a chemicallypure amorphous silica refractory fiber can be prepared. By intermixingsuch compositions with alumina, zirconia, and other refractoryglass-forming oxides, it is possible to prepare a variety of very highmelting ceramic fibers employing inexpensive, low temperature spinningequipment. Then, by simply heating the already formed fiber to asufiiciently high temperature to decompose the guanidine cation anddensify the resulting fiber, dense refractory oxide fibers can beprepared. If the heating operation is very fast, the gas created by thedecomposition of the guanidine cation can lead to the formation of afoamed fiber structure which is of exceptional value for its insulatingcharacteristics. If a dense fiber is desired, the heating can be done ata sufficiently slow rate that the gaseous decomposition products ofguanidine may be eliminated by diffusional processes Without theformation of macroscopic bubbles.

Another useful characteristic of the guanidine silicate compositions ofthe invention is that the guanidine cation can be slowly decomposed byheating in water at temperatures above 75 C. The hydrolysis of theguanidine cation leads first to the formation of urea and later to theformation of ammonium carbonate. This allows guanidine silicatesolutions to be employed as unique silica coating reagents. If it isdesired to coat a solid material with a thin amorphous silica coating,this can be done simply by contacting it or suspending it in a guanidinesilicate soluton and by heating the resulting solution.

For example, silica-coating titanium dioxide in order to minimize itsreaction with organic materials such as nylon, can be done by suspendingthe titanium dioxide pigment in a dilute solution of guanidine silicateand boiling until the decomposition or the guanidinium ion has beencompleted. As the guandine ion decomposes, reactive amorphous silica isreleased and is deposited on the solid substrate in the form of a dense,amorphous silica layer, In contrast to silica coating operations withother reagents such as by acid neutralization of alkali metal silicates,there are no impurities remaining as non-volatile contaminants in suchsilica coating operations. It is therefore not necessary to wash, todeionize, or to otherwise purify the product other than by drying, sincethe ammonium carbonate which is formed as a byproduct of the hydrolysisof guanidine silicate is completely volatile on drying, and simplydisappears from the product.

The same freedom from non-volatile impurities can be employed to giveexceptionally pure and reactive catalytic materials. For example, it isknown in the art that sodium ions are serious poisons foraluminosilicates when these are used as cracking catalysts. Exhaustivewashing and other purification techniques are therefore necessary whencracking catalysts are prepared from alkali metal silicates. This iscompletely unnecessary using the novel guanidine silicates of theinvention, since the guanidine ion may either be decomposed byhydrolysis upon heating in aqueous solution, or by firing at relativelylow temperatures. Thus, the guanidine silicates of this invention areunique materials for preparing zeolytes, aluminosilicate catalysts, andwhen used as catalyst binders in a variety of applications where alkalimetal cations are undesirble impurities.

When the compositions of this invention are employed as binders forrefractory inorganic materials such as amor phous silica grain, zicron,asbestos, fiber glass, aluminosilicates, alumina, magnesia and the like,it is possible to prepare a variety of dense, hard, strong, toughceramiclike materials possessing very high temperature resistance,exceptional strength, and yet which may be dried or cured attemperatures far below those which are commonly required to obtainceramic-like masses. Useful results are obtained with as little as 1%SiO from guanidine silicate on a solid basis. Between 3 and 25% are mostpreferred.

Specific examples of the use of guanidine silicate compositions of theinvention, the guanidine silicate-amorphous silica compositions of theinvention, and the guanidine silicate-reactive polyfunctional organiccompound compositions of the invention, as well as mixtures of thesewith one another as binders to prepare such bodies will be described ingreater detail in the examples.

Compositions of this type may be used to form massive bonded bodies aswhen guanidine silicate is employed as an adhesive and bonding agent formagnesium oxide brick, they may be employed to form hard, thin strongcoatings and films, and they may be employed to form moldingcompositions capable of being shaped by slip-casting, compressionmolding, injection molding, and a variety of other fabrication processesinto desired forms and configurations.

There are a variety of other possible uses for the compositions of thisinvention such as adhesives, fire retardants, binders, and coatingcompositions which may be applied to the surface of metals, glass,ceramics, wood and plastic. They may also be employed as binders forfibrous or particulate materials of almost any sort.

The guanidine silicate compositions could also be used for theconsolidation of said in oil drilling operations. Such a method ofconsolidation with other silicate materials is described in U.S. Patent3,175,611. The use of guanidine silicates would give a porous sandconsolidation that is inert to water, brine and oil. The guanidinesilicate could be easily decomposed at moderate temperatures to bond thesand while giving off urea and gaseous ammonia which would act as ablowing agent to give the necessary porosity. If greater porosity isneeded, additional reactants could be added, e.g., a hypochlorite, tocause a secondary gas forming reaction.

The mixtures described herein are useful as solids or in solution form,depending on case of handling and the particular application. In thesolutions, the percentage ranges referred to are based on the weight oftotal solids unless otherwise expressed.

The following examples are given by way of illustration of theinvention.

EXAMPLE 1 Seven-thousandfourteen grams of guanidine carbonate isdissolved in 28 liters of distilled water in a stainless steel tankequipped with an air stirrer. Three-thousand-fourteen grams of calciumhydroxide is added to the stirred solution and stirring is continued for14 hours at room temperature. The resulting calcium carbonate isfiltered and the filter cake washed with distilled water. The combinedfiltrate and washings weighed 33,019 grams. A sample of this is titratedto a pH of 7 with 1 normal hydrochloric acid and is found to have aconcentration of 1.98 moles of guanidine hydroxide per 1000 grams.

Four-thousand-two-hundred-eighteen grams of a hydrated amorphous silicapowder containing 93% SiO the balance being water, and having a surfacearea of 121 m. /g., is stirred into the guanidine hydroxide solution ina stainless steel tank heated on the outside of the tank with a steamcoil. The temperature is raised over a period of 3 hours from 30 C. to79 C. at which point virtually all of the silica dissolves.

This solution is cooled to room temperature and filtered to removeinsoluble material. The filtrate is vacuum concentrated at 35 to 40 C.and a vacuum of 31 inches of H 0 to a total volume of about 12 liters,having a weight of 14,257 grams. Chemical analysis shows it to contain24.01% SiO 5.81% carbon, 18.04% nitrogen. A titration with one normalhydrochloric acid shows it to have a molality of 4.30 in titratableguanidinium ions, in excellent agreement with the results from thenitrogen analysis. The mole ratio of guanidine to silica in thissolution is 1.075.

A sample of this solution is dried on a glass plate under vacuum with anitrogen purge at room temperature, and forms a water-clear, glassyfilm. This film on analysis is found to contain 37.37% SiO and 27.69%nitrogen. This checks very closely with the values of 38.71% SiO and27.10% nitrogen to be expected for a composition having the formula:

X-ray examination of this material shows it to be completely amorphous.It is also completely soluble in water in all proportions.

EXAMPLE 2 Two hundred grams of guainidine carbonate is slurried in 266mls. of distilled water and stirred in a one liter, round bottom glassflask to which is added 86 g. of calcium hydroxide. This is stirred at atemperature of 18 C. for 4 hours and the insoluble calcium carbonatewashed with 15 mls. of distilled water. The total weight of the filtrateas 274 g. 83.8 of the hydrated amorphous silica of Example 1 is added to264 g. of this guanidine hydroxide and an additional 50 ml. of distilledwater is added while the mixture is heated on a steam bath. Heating iscarried on for a 15 minute period, during which time the temperaturerises from 30 C. to 95 C. This temperature is maintained for anadditional 5 minutes, after which the solution is filtered and cooled toroom temperature with an ice bath. Chemical analysis for silica andtitration of the composition to determine the guanidine cationconcentration indicate that this composition contains 15.42% SiO and is3.55 molal in guanidine cations. The guanidine to silica mole ratio inthis composition is 1.375 to 1. This composition, as in Example 1 onevaporation to dryness yields a completely amorphous, completelywater-soluble, glassy film.

EXAMPLE 3 This is an example of one of the film-forming reactive organicmolecule-guanidine silicate compositions of the invention. Six-tenths ofa gram of the 24% SiO guanidine silicate aqueous solution prepared asdirected in Example 1 is mixed with 1 gram of an solids solutioncontaining urea and formaldehyde in the weight ratios of 60 parts offormaldehyde and 25 parts of urea in the form of their trimethylolderivative. After mixing to give a compatible solution, the product isspread on a black glass plate and dried at 70 C. to give a cross-linkedcopolymer of silicic acid, urea-formaldehyde, and guanidine which iswater-insoluble and quite hard, in distinction to the highlywater-soluble films which are formed from drying of guanidine silicatealone under these conditions.

Ten grams of a guanidine silicate-urea-formaldehyde solution as above inthe same relative proportions is mixed with 50 grams of a finely dividedsand, and this is tamped into the shape of a core in a core cavity. Thecore is set by exposure to carbon dioxide gas for a period ofapproximately 30 seconds, after which it assumes a rigid condition andis easily removable from the core cavity. The pattern is then usedimmediately to form another mold. The core is dried by heating it at C.

for 1 hour in an oven, and is used to create a cavity of the dimensionsand shape of the core in a molten metal casting. The binder burnscompletely out during the casting operation, leaving a loose sand whichis easily shaken out of the cavity in the casting.

This exemplifies the use of one of the compositions of the invention toobtain the advantage of sodium silicate-Oo -cores of setting rapidly atroom temperature to a hardness sufficient to strip them from the corepattern, and yet burning out to give easily removed sand in a fashionsimilar to that of organic resin bonded cores.

EXAMPLE 4 Ten grams of the guanidine silicate solution preparedaccording to Example 1 is mixed with 50 grams of a sized, finely dividedcore sand, as in Example 3, and this is packed into a core pattern andset with CO as described in the same example. The resulting core isemployed to produce a shaped cavity having the dimensions and shape ofthe core in a casting of molten iron, which after solidification shows acomplete disintegration of the bond to form loose sand which is easilyremoved from the cavity in the casting. The sand is reusable to formother cores in a similar type of operation.

EXAMPLE 5 This is an example of the use of one of the guanidinesilicate-colloidalamorphous silica compositions of the invention for thepurposes of preparing a mold for precision investment casting. Incontrast to the two previous examples, where it was desired to have thebond completely disintegrated, in this instance it is desirable toprepare a mold for precision investment casting which maintains itsintegrity, and it is for this reason that the mixture of colloidalamorphous silica and guanidine silicate is employed in preference topure guanidine silicate or one of the guanidine silicate-reactiveorganic molecule compositions of the invention.

One hundred grams of the guanidine silicate aqueous composition of"Example 1, containing 24% SiO is mixed in a rapidly stirred zone with56.7 'grams of a 49% solids dispersion of spherical colloidal amorphoussilica particles having an average particle diameter of 25 millimicrons,along with 19.2 grams of formamide and 20.7 grams of water. Thiscomposition is highly thixotropic. The purpose of the forrnamide is toprovide a delayed gelling operation by hydrolysis of the amide linkageand the release of formic acid to neutralize the guandine silicate.

Actually, this mixture is sufiiciently thixotropic that the degree ofthixotropic viscosity must be reduced and this is achieved by theaddition of grams of glycerol.

To this mixture is added 352 grams of a refractory grain amorphoussilica, 55% by weight of which was a size fraction which passed a 100mesh screen, but was retained on a 200 mesh screen, and 45% by weight ofwhich passed through a 325 mesh screen.

The resulting ceramic slip is fluid enough to be easily applied to thesurfaces of wax molds, and to accurately conform to the surface shapeand patterns on the surfaces of these molds. At the same time, it issufficiently thixotropic that a wax mold dipped into this solution comesout retaining an immobilized layer from A2 to A" thick of the slip inthe form of a coating which stays in place on the wax surface.

Coatings of this sort are prepared on a variety of wax patterns, and setin an oven at 50 C. which accelerates the previously noted hydrolysis ofthe formamide and caused the mixture to be converted into a firm silicagel. After curing for an hour at 50 C., the wax is melted out of thesepatterns with no cracks resulting in the coating, by steaming in a steambath at a temperature of 90 to 100 C. for a period of about 30 minutes.The molds are then dried in an oven and fired to 1000 C.

The resulting molds are porous, strong, accurate reproductions of theshape of the Wax patterns, and are employed as casting molds for molteniron and steel to produce a variety of metallic shapes which accuratelyretain the dimensions of the original wax patterns. Although thehydrolysis of the formamide in the gel formation of this composition isaccelerated in this instance by increasing the temperature to 50 C., aslow neutralization reaction with attendant gel formation occurs even atroom temperature. This same composition can therefore be sprayed againstvertical surfaces and furnish air drying completely water-insolubleceramic coatings which are useful as ceramic paints and insulatingsurfacing materials.

EXAMPLE 6 As further examples of the profound effect of adding guanidinesilicate to dispersions of colloidal amorphous silica in respect toaccelerating their gel times, it can be noted that with a solution 0.15molar in sodium chloride, the gel time of a 30% amorphous silicadispersion at pH 6 is approximately 3000 minutes. This amorphous silicadispersion contains an amount of salt in the form of sodium chloridesimilar to that which would be furnished by the acid neutralization of acomposition containing 0.15 normal guanidine silicate.

The gel time of the same concentration of an amorphous silica solutioncontaining 0.15 molar guanidine silicate at the same pH, is 64 seconds,or only one minute. Thus, its gel time is one three thousandths as longas that of an amorphous silica dispersion of the same salt content andpH which contained no guanidine silicate.

In a similar fashion, even if the concentration of guanidine silicate isonly 0.075 normal, the gel time is 274 seconds, or approximately 4 /2minutes, compared to 7500 minutes for an amorphous silica sol containingthe same concentration of sodium chloride, that would be furnished as aguanidine salt by the neutralization of this solution. Here the gel timeis changed by more than a thousand-fold by the addition of anexceedingly small amount of guanidine silicate.

It will be noted, for example, in this latter instance, that the silicaconcentration ascribable to silica coming from the guanidine silicate isonly 2.5% of the silica contained in the dispersion in the form ofcolloidal amorphous silica. Nevertheless, this 2.5% of silica in theform of guanidine silicate is capable of a thousand-fold reduction inthe gel time of the mixture.

EXAMPLE 7 One hundred grams of the 24% Si0 guanidine silicate solutionprepared as described in Example 1 is placed in a stirred flask and tothis is added 21.2 g. of acrylonitrile. This represents four-tenths of amole of acrylonitrile, or one mole of acrylonitrile for each mole ofguanidine silicate in the solution. This solution is heated withstirring until the liquid layer of acrylonitrile disappears, whichoccurs at a temperature of approximately 60 C. Simultaneously with thedisappearance of the last portion of the acrylonitrile, a copolymer gelof the acrylonitrile and guanidine silicate forms, and analysisindicates the two compositions substantially completely reacted with oneanother. The resulting polymer is a strong, rigid, threedimensionallycrosslinked interpolymer of acrylonitrile, guanidine, and silica. Thispolymer is unaffected by firing until a temperature is reached at whichthe organic materials start to decompose, after which a rigid, strongskeleton of pure silica is left behind.

EXAMPLE 8 Equal weights of the guanidine silicate liquid composition ofExample 1 containing 24% SiO and of a commercial F grade sodium silicateare mixed giving a stable solution. This is employed as a boxboardadhesive, as a plywood adhesive, and as a bonding agent for roofinggranules. In all of these applications the mixture behaves mold.

15 as a very eflicient bonding and adhesive agent, and shows a much morewater-resistant bond than that obtainable using sodium silicate alone asthe bonding agent.

EXAMPLE 9 The equipment required for preparing the refractory bricksamples consists of two steel plates 12" x 12" x /2", a mold soconstructed to contain the total prepared aggregate and withstand theforce (3000 p.s.i.) to produce a finished brick 2" x 2" x 9". The othermajor piece of equipment required is a hydraulic press capable ofexerting at least 27 tons pressure into which the completely assembledmold apparatus can be inserted. Other equipment needed is a bricklayerstrowel, spatulas, mixing box or tray and wrenches.

The mold, as shown, is open on top and bottom with the /2" steel plateserving as the bottom. The side pieces are 1" steel and the ends /2steel being bolted together with 4% D hardened steel bolts. These arefirmly tightened before any aggregate mix is transferred into thePreparation of aggregate mix A quantity of the magnesium oxide aggregatesufiicient to produce a brick 2" x 2" x 9" is weighed and transferred toa mixing tray where a predetermined Weight of binder material istroweled into it. This is applicable for both dry and/or wet binders;however, more mixing is generally necessary with wet binders toaccomplish thorough mixing. In this event, the binder should be added insmall increments. Water is then troweled into the mix until a damp, butnot wet consistency is achieved. The aggregate is then transferred intothe mold in several increments, being worked well into corners and sidesby slicing and tamping with a spatula or other suitable device. When allaggregate mix is in the mold with the surface leveled evenly, the topramming device is put in place and the complete assembly placed into thehydraulic press. (A.P.H.I. press of 30 tons capacity is used). Pressureis applied and increased to 27 tons where it is maintained until themolded brick will hold the 27 tons pressure for 1 minute.

At this time, the pressure is released and the mold assembly is removedfrom the press and disassembled. This must be done with care because atthis point the bricks are very susceptible to damage.

The finished brick is allowed to cure at room temperature for 24 hrs.after which it is cured at 250 F. for 8 hours. After the 250 F. cure, itis ready for testing for modulus of rupture (of green strength). For afired strength test the brick is fired at 1500 F. for hrs., cooledslowly to R.T., and then tested. This 1500 F. cure is accomplished inthe following manner:

Beginning at room temperature, the furnace temperature is slowlyincreased at a rate of 100 F. every 12 minutes, or 500 F. rise/hour.After it has reached 1500 F. the 5 hour cure time is begun.

For test procedure, refer to ASTM Designation C133- 55, Standard Methodsof Test for Cold Crushing Strength and Modulus of Rupture of RefractoryBrick and Shapes.

Mixtures of varying amounts of guanidine silicate and MgO are formed andpressed into brick according to the described procedure. After firing atthe prescribed temperature and manner the following limits were observedas practical optimum regions for binder (guanidine sili cate) and H 0levels: 3-6% (guanidine silicate) and 3-6% H O.

Within this region the modulus of rupture for bricks formed with 6%guanidine silicate and 3.75% H O was 690 lb. M of R after 1500 F. fireand 960 M of R after 2500 F. fire.

The great advantage in using guanidine silicate as a binder for MgO isthat no fluxing agent is present in the binder. At the temperatureswhich the bricks are fired the guanidine silicate decomposes to leavepure silica which does not act as much of a fluxing agent for MgO asions from the Group I elements of the periodic chart. The molecularsilica is a very good bonding agent.

EXAMPLE 10 A composition having a mole ratio of 0.863 mole of guanidineto one mole of silica and containing a silica concentration of 23.7%,was prepared by the procedure of Example 1, by appropriate adjustment inthe molar concentration of guanidine employed.

A series of concentrated guanidine silicates of lower ratios can then beprepared, to illustrate the stability of such compositions.

Four hundred fifty-six grams of the 0.863 mole ratio guanidine silicateare mixed in a high speed laboratory blender with 150 g. of a deionizedcolloidal silica 01 having a concentration of 40% SiO by weight whichhas a surface area of 231 m. g. The sol is prepared from a commerciallyavailable, alkali-stabilized, spherical amorphous silica sol of 40%concentration by removing the stabilizing ions by contacting the solwith the hydrogen form of a cation exchange resin.

This mixture is then placed on a steam bath, and in about 15 minutes allof the colloidal silica has gone into solution and a water-clear productwith no turbidity is obtained. Corresponding to the larger quantity ofthe acidic silicate anions, the pH of this material is 11.3, comparedwith a value of 11.8 for the starting guanidine silicate having an 0.863to 1 mole ratio of guanidine to silica. The calculated guanidine tosilica mole ratio of this material is 0.55. It is noted that after threedays this material becomes exceedingly viscous and ultimately solidifiesinto a gel containing a network of white, waterinsoluble gel phase.

The above procedure is repeated employing the same guanidine silicatestarting material, only the relative proportions in this instance are600 g. of the starting guanidine silicate and 133 g. of the deionizedcommercial amorphous silica sol. Again, this material clears upcompletely after about 15 minutes heating on the steam bath, and thismaterial remains stble for longer period of time than the previous one.It takes about 13 days until the viscosity increases to a point that itcan no longer be poured. Even at this stage, the major portion of it issoluble in water, but it is found that within a matter of 2 or 3 hoursafter dissolving this gelled 40% material to furnish about a 10%solution, a flocculant colloidal white precipitate settles out ofsolution. The mole ratio of guanidine to silica in this composition is0.62.

If procedures of these examples are repeated with a further adjustmentof the ratio of colloidal silica to guanidine silicate, a material isobtained having a mole ratio of 0.70 of guanidine to silica. Thismaterial is stable indefinitely upon storage at room temperatures andundergoes no discernible change even after several ,months.

EXAMPLE 11 Guanidine silicate by itself is an excellent coating materialalthough it is water sensitive. Stepwise treatment of steel panels firstwith guanidine silica then with formaldehyde or a difunctional moietysuch as maleic acid and heating in an open flame or oven leaves a hardwater insensitive coating. A 1 mil wet thickness of a 30% solution ofguanidine silicate is applied to a steel panel and allowed to dry. Thecoating is then covered with a 37% solution of formaldehyde and isheated at C. for /2 hour. The resulting coating is hard, clear, waterinsensitive, and adheres very well to the steel.

What is claimed is:

1. A composition of matter consisting essentially of amorphous, ionicguanidine silicate, said guanidine silicate having a mole ratio ofguanidinium cations to silicate anions of from 1.5 to 0.65 and beingsoluble in water to the extent of at least 15% by weight of silica fromsaid amorphous guanidine silicate based on the total weight of solution.

2. A composition for use as a binder for refractory 1 7 particlescomprising the composition of claim 1 and from 2080 percent by weight ofan organic binding resin based on the Weight of the total binder solids.

3. A composition as described in claim 2 wherein said organic bindingresin is selected from the group consisting of phenol-formaldehyderesins, furfural resins, furfural phosphoric acid resins andfurfural-urea formaldehyde resins.

4. A composition of matter consisting essentially of a stable, aqueoussolution of amorphous guanidine silicate, said guanidine silicate havinga mole ratio of guanidinium cations to silicate anions of from 1.5 to0.65, said solution being characterized in that it contains at least 15%by weight of silica from said amorphous guanidine silicate.

5. A process for the preparation of non-crystalline guanidine silicatecompositions characterized by readywater solubility comprisingcontacting a source of guanidinum ions with a source of silicate ions,

maintaining the molar ratios of guanidinium ions to silicate ions withinthe range of from 1.5 to 0.65,

at a pH between 10.5 and 14 and a temperature of from to C. in aqueousmedium for from 10 seconds to 24 hours, followed by concentration.

References Cited UNITED STATES PATENTS 3,338,901 8/1967 Weldes 2602683,428,465 2/1969 McLeod 10638.35 2,224,815 12/ 1940 Glycofrides 260372,689,245 9/1954 Merrill 260247 WILLIAM H. SHORT, Primary ExaminerHOWARD SCHAIN, Assistant Examiner US. Cl. X.R.

